Amazon Milk Frog

AmphibianSouth America

10 Mar

Written By Alexander Julius Jensen

Trachycephalus resinifictrix

The Amazon milk frog isn't named for its milky white appearance, instead, its name refers to a poisonous milky substance that it secretes when threatened. It also uses the fluid as "sunscreen" — lathering it over its body to prevent itself from drying out in the sun.

Milk & Chocolate

A young Amazon milk frog looks like an artfully crafted confection from a luxurious box of chocolates. Its skin is smooth and lacquered, shining like a perfectly tempered treat. A creamy white base swirls with bands and swathes of rich cocoa brown. But this frog isn't named for its milky white skin, and that's just as well, since its lighter skin patches can often appear blue or green tinted — because this frog has blue blood (it isn't an aristocrat, it's literally got blue blood). It also loses much of its lustre with age: its creamy white becomes a dull grey and its sumptuous dark cocoa bands, like chocolate left out too long, become pale and speckled white. By the time it's an adult, it no longer looks like a dainty dessert. One of the largest frogs in South America, it can grow to be 10 centimetres (4 in) long. And, as it gets older, its once smooth skin becomes more and more lumpy, like curdling milk. It's as if the frog goes through a long process of expiration — which in a way, like all of us, it does — it's just got a long "best-before date", living for over 15 years in the wild and up to 25 in captivity.

Toxic Sunscreen

No, it's not named for the appearance of its skin, but for what it secretes through its skin. When the frog feels threatened, specialised glands can produce a white and sticky fluid that looks enough like milk to warrant the name "milk frog" (the alternative name would have been less than appropriate). This isn't a milk you'd want to drink, however, as the substance is poisonous and acts as a deterrent to potential predators — it likely won't kill you, since it's not as potent as some other frog toxins, but it is enough to make predators sick. Not only is this substance a predator-repellent, but it's also sunscreen. The milk frog will smear it all over its body to assist with moisture retention and prevent its body from drying out in the sun.

Crappy Camouflage

Another, much less appetizing but probably more apt, analogy for this frog's appearance is that of bird droppings. This isn't a dig at the frog. Birdshit mimicry is a tried and tested method for camouflage, found across many branches of the animal kingdom. The giant swallowtail, the largest butterfly in North America, adorned with striking yellow patterns on inky wings, has a less-than-beautiful start to its life. As a caterpillar, it is lumpy, moist-looking, and coloured in dark browns and white — when it isn't moving, it looks like it was recently discharged by a bird. The "bird-dropping spiders" (Celaenia excavata and Phrynarachne decipiens) are a pair of more leggy-looking splotches of bird poop. And other frogs employ this strategy too, with beautiful effectiveness, such as the species known scientifically as Theloderma asperum, and informally as the "bird poop frog".

Bird droppings on leaf litter or aposematic warning?

Animals don't evolve their appearances for aesthetic appreciation by the human eye. In the aforementioned cases, they evolved for the purposes of camouflage, to hide and avoid being eaten. And what's more unappetizing than a piece of shit. The Amazon milk frog must survive in the lively environment of its namesake rainforest — ranging throughout northeastern South America. It is a member of the family Hylidae, a group of over 700 species commonly known as tree frogs (and allies). The milk frog does indeed have an arboreal disposition, rarely ever setting foot on the ground. Wide pads tip each of the frog's toes, providing it with such great adhesion that can hold up 14 times its own body weight. It revels in the thick, humid air of the rainforest canopy, with its permeable skin exchanging more oxygen while moist (assisted by its milky "sunscreen"), and it's most often found near water; whether that be slow-moving streams or just little pools that accumulate in tree cavities. Perhaps, with a poisonous concoction coating its skin, it has little reason to hide — aposematism, the phenomenon wherein toxic animals advertise themselves with bright conspicuous colours, is readily used by its poison dart frog neighbours — but during the day, when the Amazon milk frog rests, it still likes to hide beneath leaves and other vegetation — where it can, if discovered, do its best impression of bird dropping.

Golden Eyes

As night falls, the milk frog stirs. Its prominent eyes — with horizontally slit pupils and ringed with irises of glowing copper, suffused with inky stains — search the dark for insects, invertebrates and other small amphibians (its eye's intense colours also give the frog its alternate name of “mission golden-eyed tree frog"). It doesn't shoot its tongue to snag prey, but hides and ambushes its unwary victims; bounding upon them and using its front limbs to shove them in its cavernous blue mouth. Sticky saliva prevents its meal from escaping by binding it in a viscous trap, but it also makes prey hard to swallow. Those beautiful big eyes that sighted the prey also help in swallowing it. The frog pushes its eyeballs down into its mouth cavity — in the equivalent of a froggy blink — creating pressure, liquefying its saliva, and forcing its food down its throat.

“Canoe Frogs” & Romantic Deception

The unlit rainforest reverberates with the calls of milk frogs. In Brazil, the species is also known as "sapo canoeiro", or the "canoe frog", because its croak is reminiscent of oars tapping the side of a canoe. Many of them together sound like a ghostly procession of boats in the night. During the rainy season, males call for attention, croaking loudly for the female frogs to hear. A female appears from the gloomy foliage and the male directs her towards nearby water — only for this event will milk frogs leave their arboreal homes. She lays some 2,000 eggs in a gelatinous heap and he diligently fertilizes them. Neither the male nor the female care for their offspring, but the male may provide them with a leg up. After having fertilised the eggs, he keeps calling, promising romance (and his sperm) to entice another nearby female. Another female does indeed arrive. And she too lays her eggs: a large batch near the already fertilized progeny. This is where the male makes his betrayal. He doesn't fertilize her eggs, leaving them barren and lifeless — a stockpile for his progeny to feed on once they hatch. They do so within one day, proceeding to consume their would-be step-siblings, and spend the next three to five weeks metamorphosing into milk-chocolate frogs, beautiful while their youth lasts.

**Where Does It Live?**

⛰️ Rainforests canopies.
📍 Northeastern South America; Ecuador, Venezuela, Colombia, Peru, Bolivia, Guyana, French Guiana, Suriname and Brazil.

‘Least Concern’ as of 13 April, 2020.

IUCN

Size // Small
Length // 10 cm (4 in)
Weight // N/A
Activity: Nocturnal 🌙
Lifestyle: Solitary 👤
Lifespan: 5 years (in the wild), up to 25 (in captivity)
Diet: Carnivore
Favorite Food: Insects 🐜
Class: Amphibia
Order: Anura
Family: Hylidae
Genus: Trachycephalus
Species: T. resinifictrix

Despite often appearing white, the lighter parts of its skin are actually tinted blue or green — this is because of its (literally) blue blood.

Its beautiful golden eyes give it its alternate name of “mission golden-eyed tree frog". The inside of its mouth is also a striking blue.

As this frog ages, its colours fade and the surface of its skin becomes more bumpy.

It can live for over 15 years in the wild and up to 25 in captivity.

Growing to be 10 cm (4 in) long, it is one of the larger frogs in South America.

In addition to using its milky secretion as predator deterrence — enough to make a predator sick but unlikely to kill them — this frog will also rub it over its body as it serves to prevent moisture loss when in the sun or during drier conditions.

These frogs will rarely venture to the ground, seemingly the only exception being during breeding.

A male will call loudly to advertise his presence to females. After he mates with one, she lays her roughly 2,000 eggs near some water and he fertilizes them. But he keeps calling for other females and when one arrives, she lays her eggs next to the first batch — the male, however, doesn't fertilize these. Instead, the second batch of eggs serves as a meal for his young when they hatch.

In Brazil, the milk frog is also known as "sapo canoeiro", or the "canoe frog", because its croak is reminiscent of oars tapping the side of a canoe